The so-called Meat Gu was actually a special Gu the sect cultivated. It could swallow all kinds of things to grow, and it could increase in size as well. Even if one cut off a chunk of its flesh, it would rapidly regrow as long as there was enough food.
Previously, because Yin Ling's Blood Pills had been snatched, her Bloodthirsty Gu had almost sucked her dry. Thus, she ended up selling her body and seemed to follow a senior outer disciple.